Field of the Invention
The present invention relates to an image pickup apparatus capable of changing a drive mode, which is equipped with an image pickup sensor capable of simultaneously outputting image signals from two or more paths, and an image signal control method executed by the image pickup apparatus.
Description of the Related Art
Examples of an image pickup apparatus using an image pickup device, such as a CCD sensor and a CMOS sensor, include one equipped with a live view function. The live view function is a function that makes it possible to check an object image by sequentially displaying images based on image signals continuously read out from the image pickup device, on a display device, such as a liquid crystal display provided e.g. on a rear surface of the image pickup apparatus.
In a case where a battery is used as a power source of the image pickup apparatus, it is desirable to reduce power consumption for the live view display in a photographing standby state, but on the other hand, there is a case where high definition live view display is desired. To cope with this, there has been proposed a technique for switching a live view-displaying method between a live view display in a non-operated state and a live view display in a photographing preparation state (e.g. a state in which a shutter button is half pressed for an AF operation and the like on an object).
A technique for realizing the high-definition live view display has been proposed by e.g. Japanese Patent Laid-Open Publication No. 2012-105225. In Japanese Patent Laid-Open Publication No. 2012-105225, exposure time for pixels is controlled to be different between pixel areas, i.e. on a row-by-row basis, for example, to thereby acquire high-sensitivity pixel information and low-sensitivity pixel information, and output pixel values are determined based on these different types of pixel information representing respective different sensitivities to thereby make it possible to generate a wide dynamic range image.
However, to switch the live view display between the low image quality display in a low power consumption mode and a high definition display for photographing preparation, it is necessary to change the photographing drive mode for the live view. A time lag occurs when the photographing drive mode for the live view is changed, and hence the live view images cannot be obtained during the time lag, which causes freezing of the live view display or a recorded moving image (phenomenon that the same image is continuously displayed over an extended time period or the same image is continuously recorded).
Further, in the conventional image pickup apparatus, when a photographing drive mode for live view display or recording of a moving image is changed e.g. according to a change of a photographing view angle (angle of view), a time lag is generated when the photographing drive mode is changed similarly to the above, which makes it impossible to obtain images during the time lag. This causes the above-mentioned freezing of the live view display or the recorded moving image.
There has been proposed a technique for coping with this problem e.g. in Japanese Patent Laid-Open Publication No. 2007-228433. In the technique described in Japanese Patent Laid-Open Publication No. 2007-228433, an image pickup apparatus configured to perform image magnification by changing the photographing drive mode according to an electronic zoom magnification, performs gain correction dependent on a difference in exposure time on image data obtained before and after changing the photographing drive mode, for each readout row of pixels of the image pickup device. According to this processing, there is obtained image data for the live view display or the moving image recording, which is formed by giving continuity to image data items obtained before and after changing the photographing drive mode.
However, the technique described in Japanese Patent Laid-Open Publication No. 2007-228433 has a problem that the gain correction control performed in changing the photographing drive mode becomes complex. Further, there is a fear that the image quality of frame images obtained after the correction is degraded compared with the image quality of other frames which are not corrected, due to factors including a difference in gains used for the gain correction, which vary between areas.